The present invention relates to a radar sensor and a radar antenna, which are particularly suitable for monitoring the vicinity of a motor vehicle.
Such radar sensors are needed for various comfort-related and safety-related driver-assistance systems. They use sensors aligned in the forward direction of travel, in order to gather information about the traffic and obstacles on the road. This information these information items are used by the corresponding driver-assistance system, in order to implement automatic vehicle-to-vehicle ranging or to carry out an automatic emergency-braking function, or for applications from the area of adaptive driving control, collision prevention, and for the future, autonomous driving of vehicles.
Described in IEEE Transactions on Microwave Theory and Techniques, VOL. 45, NO. 12, December 1997, xe2x80x9cMillimeter-Wave Radar Sensor for Automotive Intelligent Cruise Control (ICC)xe2x80x9d, M. E. Russell et al., is a radar sensor, which has a control circuit and a radar antenna, the control circuit being in the form of a transceiver module, and the radar antenna being connected to the control circuit by at least one lead. In this context, a part of the control circuit is in the form of an MMIC (monolithic millimeterwave integrated circuit). In addition, the radar antenna is in the form of a printed circuit and has a Rotman lens and a group antenna. The Rotman lens has a lenticular parallel-plate line, at least two supply leads, a plurality of coupling leads, and delay lines. In addition, the group antenna is made of a plurality of individual antennas, which are connected in series in at least two rows. Each of these rows of individual antennas is connected to a delay line, which transmits the high-frequency signal supplied by the parallel-plate line to the associated coupling lead, to the row of individual antennas.
In the case of the radar sensor represented above, there is a problem with the connection or coupling of the MMIC modules to the radar antenna, since differently dimensioned circuits situated on different substrates must be interconnected. In this case, losses often occur, since the connecting lines are not optimally adapted for the transmission of high-frequency signals.
A further disadvantage of the conventional radar antenna is that, in the case of transmitting high-frequency signals between the group antenna and the Rotman lens, a defined phase relation is indeed present between the specific rows of the individual antennas and the associated coupling leads of the Rotman lens. However, a variable amplitude distribution of the high-frequency signals to the separate rows of individual antennas of the group antenna is not possible in this radar antenna. Thus, the directional characteristic of the group antenna cannot be adjusted in an optimum manner.
In addition, the above-described conventional radar antenna has the problem of the entire radar sensor occupying a large volume, due to the Rotman lens and the group antenna being positioned at right angles to each other. Therefore, the dimensional requirements for a radar sensor cannot be fulfilled to an extent satisfactory for, e.g., positioning it in the region of the bumper of a motor vehicle.
Therefore, it is an object of the present invention to provide a radar sensor and a radar antenna in which the previously described disadvantages are eliminated.
According to a first aspect of the present invention, the above-mentioned engineering problem is solved by providing a radar sensor having a control circuit, which is in the form of a transmitting and/or receiving module and has at least one MMIC (monolithic millimeter-wave integrated circuit), and having a radar antenna, which is connected to the control circuit by at least one lead and has a Rotman lens and a group antenna, the control circuit and the radar antenna essentially being positioned in parallel with each other.
The planar form of the entire radar sensor results in a more compact construction occupying a smaller volume, so that the radar sensor of the present invention may be easily integrated into the region of the bumper of a motor vehicle.
An example embodiment of the present invention provides for a conductor support, lines for transmitting high-frequency signals between the control circuit and at least one lead of the radar antenna being situated on the conductor support, and the conductor support being situated between the control circuit and the radar antenna.
The above-mentioned construction of the radar sensor allows the signal transmission between the variably dimensioned modules, e.g., the at least one MMIC component and the radar antenna, to be effectively implemented by an additional module. To this end, the lines situated on the additional conductor support may be manufactured prior to assembling the radar sensor, and therefore, the actual connections between the at least one MMIC component and the radar antenna may be manufactured in a simple manner, after assembly, including that of the conductor support. This ensures that the lines arranged on the conductor support are suitably dimensioned at their points of connection to the least one MMIC component and to the radar antenna.
In this context, the lines on the conductor support may essentially extend in one plane, parallelly to the printed circuit traces of the control circuit and to the at least one lead of the radar antenna. If these lines are also positioned essentially at the same elevation as the control circuit and the radar antenna, then the result is a configuration of the different line elements, which essentially extend in one plane. The consequently produced, electrical and electromagnetic connections between the different modules are therefore reduced to a minimum, so that occurring losses are minimized.
The lines may be in the form of microstrip transmission lines on the conductor support, which may be particularly suited for transmitting high-frequency electromagnetic signals.
A further example embodiment of the present invention provides for a circuit support, to which the at least one MMIC component of the control circuit, the conductor support, and at least part of the radar antenna are connected, e.g., using an adhesive. Therefore, the circuit support may also be referred to as a multichip module. Thus, a unit is formed by all of the components, which are interconnected by a circuit support. In addition, transmission lines for transmitting signals between the lines of the conductor support and the supply leads of the radar antenna may also be formed on the circuit support. Thus, the circuit support also assumes tasks that are partially functional.
On one hand, wire-bonding connections, and on the other hand, electromagnetic field couplings are possible as options for a connection between the lines of the conductor support and the at least one lead of the radar antenna. In the case of the wire-bonding connection, the connecting elements may be cut in a highly exact manner, since the electrical properties of the wire-bonding connection substantially depend on its precision. In addition, a connection using electromagnetic field coupling allows higher manufacturing tolerances of the individual elements, but requires more expenditure for circuit design.
An advantage of the above-mentioned configuration is the modularity, for different control circuits in the form of pre-fabricated MMIC components may be used with the same radar antennas for different application purposes. The assembly and connection are performed on the circuit support.
In addition, it should be pointed out that the arrangmenet of the above-described, present invention is independent of the particular form of the radar antenna.
According to a second aspect of the present invention, the above-mentioned engineering problem is solved by a radar antenna including a Rotman lens having a lenticular parallel-plate line, at least two supply leads, a plurality of coupling leads, and delay lines, and including a group antenna having a plurality of individual antennas, which, in each case, are connected in series in at least two rows. Each row is connected by an antenna terminal to a delay line, which transmits the high-frequency signals supplied by the parallel-plate line to the corresponding coupling lead, to the row of individual antennas. The lengths of the delay lines are selected for a predetermined frequency of the high-frequency signal, in such a manner, that, in response to the high-frequency signal being applied to each of the supply leads, signals having a predetermined phase distribution are applied to the antenna leads. For a predetermined frequency of the high-frequency signal, the signal propagation delays, which occur between the supply leads and the antenna leads, are changed by an essentially integral multiple of the signal period, for different delay lines, in order to preselect an amplitude distribution of the signals applied to the antenna terminals.
In this context, the signal propagation times for outer delay lines may be lengthened in comparison with inner delay lines. An advantage of this refinement is that, in comparison with the conventional radar antenna, not only is a suitable phase occupancy achieved at the rows of individual antennas of the group antenna, but it is possible to selectively set the amplitude distribution of the signals applied to the rows of individual antennas, as well.
In this context, different geometric lengths of the delay lines predetermine the signal propagation times along the delay lines. However, it is possible to preselect the signal propagation times along the delay lines, using different dielectric constants for the substrates utilized for the delay lines. The high-frequency signals having a phase relationship predetermined by the supplied signal may be sent to the different rows of individual antennas. This is possible due to the narrow-band characteristic of the high-frequency signal to be transmitted, since the frequency differences within the band width of the high-frequency signal only result in negligible phase differences based on different signal propagation times. This allows a very precise directivity characteristic to be achieved for the group antenna.
According to a third aspect of the present invention, the above-mentioned engineering problem is solved by a radar antenna including a Rotman lens having a lenticular parallel-plate line, at least two supply leads, a plurality of coupling leads, and delay lines, and including a group antenna having a plurality of individual antennas, which, in each case, are connected in series in at least two rows. The Rotman lens and the group antenna are positioned so as to be essentially parallel to each other and spaced apart.
This arrangement may achieve a space-saving configuration of the Rotman lens and group antenna, so that a planar design of the radar antenna and the radar sensor is possible, thereby simplifying their use in a motor vehicle. Thus, it is possible, for example, to integrate a flat radar sensor and a flat radar antenna into the bumper of a motor vehicle. The radar sensor includes the arrangement of the Rotman lens and the group antenna next to each other on a substrate.
The Rotman lens and the group antenna may be formed on two different substrates, the sides of the two substrates facing away from the Rotman lens and the group antenna being connected to each other, and a common metallic coating being situated between the two substrates. This metallic layer may be used as a common ground for the Rotman lens and the group antenna.
Coupling slits may be formed in the metallic layer, which electromagnetically couple the antenna terminals of the rows the group antenna""s individual antennas, to the connection points of the delay lines. Two important advantages are associated with this. First of all, there is no need to produce a metallic connection between the delay lines and the rows of individual antennas. Secondly, the electromagnetic field generated by the Rotman lens only affects the group antenna at the coupling slits provided for this purpose. In addition, the metallic layer is used as a shield between the Rotman lens and the group antenna.
The connection points of the rows of individual antennas may be essentially situated in the center of the rows, whereby a symmetric amplitude distribution to the individual antennas inside a row of individual antennas is achieved. This further improves the directivity characteristic of the radar antenna.
Additional features and advantages of the present invention are explained in detail in the following description of example embodiments.